This invention relates to a polymer latex in which the arrangement of the polymer molecules in the latex particle is novel. The latexes are useful in the formation of coatings, adhesives and binders. They are particularly useful to supplant combinations of polymers and coalescents in polish and coatings compositions. The polishes or coatings may be applied to either hard or soft surfaces and are especially useful for application to flooring and wall surfaces to form clear coatings having a glossy appearance.
The polymer in a film-forming latex is required to be soft enough to form a film of good integrity yet hard enough so the film has high strength, low dirt pick-up and a myriad of other related properties depending on the specific application. It is known that if the glass transition temperature (Tg) of the polymer is below the temperature at which the film is being formed, a film of good integrity, that is, not "cheesy", is normally produced on drying a latex. However, the very softness of the latex particles which leads to good film formation means that the produced film is soft or tacky as opposed to being strong, hard, wear resistant and tough. The art recognized way out of the dilemma of having a polymer which is soft enough to form a well integrated film yet hard enough to form a useful film is to add coalescents volatile enough to leave the film after film formation has occurred. With the advent of greater concern about air pollution, there has arisen the need to eliminate the volatile coalescents if possible. Elimination of the coalescents is also economical, the cost of the coalescent being saved.
Another approach toward preparing high Tg polymers with low minimum film formation temperatures (MFT) is the incorporation of a high proportion of hydrophilic monomers (e.g. those with hydroxyl, amine or carboxyl functions) in the polymer. This induces water swelling of the latex particles which simultaneously softens the particle in the latex. At normal polymer concentrations the swelling is accompanied by very high viscosities particularly if the storage or use pH is such that the carboxylic groups or amine groups are neutralized or partially neutralized. A further disadvantage is water sensitivity of the final film as well as sensitivity to acidic or basic solutions. Polymers of hydrophilic monomers made by solution polymerization procedures and applied in solution are taught by J. Weiss in U.S. Pat. No. 3,935,368 for use in coating vinyl chloride flooring materials.
Still another solution to the problem of getting hard coating in the form of a well integrated film is that of D. Schoenholz et al. in U.S. Pat. No. 3,949,107. Schoenholz teaches applying a polish containing an aqueous dispersion of a resin with a Tg of 30.degree. C. to 80.degree. C. to a floor, having either the polish or the floor preheated to a temperature above the Tg of the resin.
This disclosure teaches a latex low enough in viscosity to make suitable formulations for application and which, without coalescents, is film forming and produces tough, hard films.